问遇到一个奇怪的错误: Object Gruntfile.js没有方法'flatten‘

EN

$ cat xx
$ grunt

/home/cl/node_modules/grunt/node_modules/findup-sync/lib/findup-sync.js:33
    }).flatten().uniq().value();
       ^
TypeError: Object Gruntfile.js has no method 'flatten'
    at Object.module.exports [as findup] (/home/cl/node_modules/grunt/node_modules/findup-sync/lib/findup-sync.js:33:8)
    at Task.task.init (/home/cl/node_modules/grunt/lib/grunt/task.js:414:16)
    at Object.grunt.tasks (/home/cl/node_modules/grunt/lib/grunt.js:113:8)
    at Object.module.exports [as cli] (/home/cl/node_modules/grunt/lib/grunt/cli.js:38:9)
    at Object.<anonymous> (/usr/lib/node_modules/grunt-cli/bin/grunt:41:20)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)

/*
 * findup-sync
 * https://github.com/cowboy/node-findup-sync
 *
 * Copyright (c) 2013 "Cowboy" Ben Alman
 * Licensed under the MIT license.
 */

'use strict';

// Nodejs libs.
var path = require('path');

// External libs.
var glob = require('glob');
var _ = require('lodash');

// Search for a filename in the given directory or all parent directories.
module.exports = function(patterns, options) {
  // Normalize patterns to an array.
  if (!Array.isArray(patterns)) { patterns = [patterns]; }
  // Create globOptions so that it can be modified without mutating the
  // original object.
  var globOptions = Object.create(options || {});
  globOptions.maxDepth = 1;
  globOptions.cwd = path.resolve(globOptions.cwd || '.');

  var files, lastpath;
  do {
    // Search for files matching patterns.
    files = _(patterns).map(function(pattern) {
      return glob.sync(pattern, globOptions);
    }).flatten().uniq().value(); // <--------- OFFENDING LINE
    // Return file if found.
    if (files.length > 0) {
      return path.resolve(path.join(globOptions.cwd, files[0]));
    }
    // Go up a directory.
    lastpath = globOptions.cwd;
    globOptions.cwd = path.resolve(globOptions.cwd, '..');
  // If parentpath is the same as basedir, we can't go any higher.
  } while (globOptions.cwd !== lastpath);

  // No files were found!
  return null;
};

$ ls -l node_modules/
total 20
drwxrwxr-x. 6 a a 4096 Oct  2 00:42 grunt
drwxrwxr-x. 4 a a 4096 Oct  2 00:42 grunt-contrib-compass
drwxrwxr-x. 6 a a 4096 Oct  2 00:42 grunt-contrib-jshint
drwxrwxr-x. 6 a a 4096 Oct  2 00:42 grunt-contrib-watch
drwxrwxr-x. 4 a a 4096 Oct  2 00:42 grunt-dustjs

$ npm list
prepscholar@0.0.0 /home/a/prep/main/web/client
├─┬ grunt@0.4.1
│ ├── async@0.1.22
│ ├── coffee-script@1.3.3
│ ├── colors@0.6.2
│ ├── dateformat@1.0.2-1.2.3
│ ├── eventemitter2@0.4.13
│ ├─┬ findup-sync@0.1.2
│ │ └── lodash@1.0.1
│ ├─┬ glob@3.1.21
│ │ ├── graceful-fs@1.2.3
│ │ └── inherits@1.0.0
│ ├── hooker@0.2.3
│ ├── iconv-lite@0.2.11
│ ├─┬ js-yaml@2.0.5
│ │ ├─┬ argparse@0.1.15
│ │ │ ├── underscore@1.4.4
│ │ │ └── underscore.string@2.3.3
│ │ └── esprima@1.0.4
│ ├── lodash@0.9.2
│ ├─┬ minimatch@0.2.12
│ │ ├── lru-cache@2.3.1
│ │ └── sigmund@1.0.0
│ ├─┬ nopt@1.0.10
│ │ └── abbrev@1.0.4
│ ├─┬ rimraf@2.0.3
│ │ └── graceful-fs@1.1.14
│ ├── underscore.string@2.2.1
│ └── which@1.0.5
├─┬ grunt-contrib-compass@0.5.0
│ ├── async@0.2.9
│ ├── dargs@0.1.0
│ └── tmp@0.0.21
├─┬ grunt-contrib-jshint@0.6.4
│ └─┬ jshint@2.1.10
│   ├─┬ cli@0.4.5
│   │ └─┬ glob@3.2.6
│   │   └── inherits@2.0.1
│   ├── console-browserify@0.1.6
│   ├─┬ minimatch@0.2.12
│   │ ├── lru-cache@2.3.1
│   │ └── sigmund@1.0.0
│   ├── shelljs@0.1.4
│   └── underscore@1.4.4
├─┬ grunt-contrib-watch@0.5.3
│ ├─┬ gaze@0.4.2
│ │ └─┬ globule@0.1.0
│ │   ├─┬ glob@3.1.21
│ │   │ ├── graceful-fs@1.2.3
│ │   │ └── inherits@1.0.0
│ │   ├── lodash@1.0.1
│ │   └─┬ minimatch@0.2.12
│ │     ├── lru-cache@2.3.1
│ │     └── sigmund@1.0.0
│ └─┬ tiny-lr@0.0.4
│   ├── debug@0.7.2
│   ├── faye-websocket@0.4.4
│   ├─┬ noptify@0.0.3
│   │ └─┬ nopt@2.0.0
│   │   └── abbrev@1.0.4
│   └── qs@0.5.6
└─┬ grunt-dustjs@1.1.1
  └── dustjs-linkedin@2.0.3

$ cat package.json 
{
  "name": "prepscholar",
  "version": "0.0.0",
  "devDependencies": {
    "grunt": "~0.4.1",
    "grunt-contrib-jshint": "~0.6.4",
    "grunt-dustjs": "~1.1.1",
    "grunt-contrib-watch": "~0.5.3",
    "grunt-contrib-compass": "~0.5.0"
  }
}

$ cat Gruntfile.js 

module.exports = function(grunt) {

  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    jshint: {
      files: ['Gruntfile.js', 'app/js/**/*.js', '!app/js/lib/**/*.js']
    },
    dustjs: {
      compile: {
        src: ['app/templates/**/*.html'],
        dest: 'app/js/templates.js'
      }
    },
    compass: {
      dev: {
        options: {
          sassDir: 'app/sass',
          cssDir: 'app/css',
          imagesDir: 'app/img',
          fontsDir: 'app/fonts',
          javascriptsDir: 'app/js/app',
          outputStyle: 'compressed'
        }
      }
    },
    watch: {
      gruntfile: {
        files: 'Gruntfile.js',
        tasks: ['compile']
      },
      css: {
        files: 'app/sass/**/*.scss',
        tasks: ['compass:dev']
      },
      livereload: {
        options: { livereload: true },
        files: ['app/css/**/*']
      },
      dust: {
        files: 'app/templates/**/*.html',
        tasks: ['dustjs']
      }
    }
  });

  grunt.loadNpmTasks('grunt-contrib-jshint');
  grunt.loadNpmTasks('grunt-contrib-compass');
  grunt.loadNpmTasks('grunt-contrib-watch');
  grunt.loadNpmTasks('grunt-dustjs');
  grunt.loadNpmTasks('underscore');

  grunt.registerTask('default', ['compile', 'watch']);
  grunt.registerTask('compile', ['dust', 'compass']);
  grunt.registerTask('dust', ['dustjs']);
  grunt.registerTask('lint', ['jshint']);
};